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Superchlorinate or Shock with Bleach

Folks

I've got a new SWCG pool that's coming up on requiring it's first shock for Combined Chlorine (No Algae)
I have read in other posts that the superchlorinate function of the SWCGs can reduce the effective lifespan of the cell and that it may just be best to hit the pool with regular bleach to shock it.

A few questions:
Is the above statement true and is bleach the best way to go?
How long do I need to hold the FC above 15 (CYA is 40 so FC 15 is my shock level)? Just until the CC test reads zero?
Do I run the SWCG at a normal level throughout the shock process or turn it off?
Is it necessary to bring the FC level down quickly after the shock or just let it burn off.

Your numbers look really good. Your FC level is a bit high for your CYA of 40. I have a CYA of 35-40 and keep my FC at 3.0
your CC of .5 is right on the edge of needing to superchlorinate. Chances are that if you don't have a heavy bather load, lots of sun or lots of rain you can get by without shocking. If you want to shock with bleach you can just keep your SWG running normally. Since there is no sign of algae, you can shock to the desired level 15ppm and I would just let it burn off back to normal levels and retest for CC. You might want to turn down your SWG a little as 7ppm is a bit high to keep your FC at.

Yes, from what i hear, the more you can save from shocking with your SWG, the longer it will last.

I have a similar size pool to yours but vinyl and also running a IG20 instead of your 40. I have my % set at 40.

I do have a low bather load so I will hold off on the shock until the CC tests at 1.0 and then hit it with the bleach.

I am having problems maintaining a consistent FC level with my SWCG.
I am using the FAS-DPD test daily to try and get an accurate result and adjust the SWCG output daily, if required.
I seem to get it stable for a few days and then the sun will go in for a day (like it did yesterday) and my FC shoots up from 4.5 to 7.0 in a day.

I will admit at this point that my Salt level is high (my error) at 4300ppm and that I have been toying with adding more CYA to see if I can get the FC more stable. Any experience you can share on this subject too would also be appreciated!

Don't be too surprised if you don't ever get to 1.0 CC's .5 is quite common in a healthy pool and not an indicator that's it's absolutely headed for 1.0 or more. So, you've got CC's less than 1.0, clear water, and (presumably) the ability to hold FC overnight.......That's the three indicators that chemgeek talks about that say you have a healthy pool.

Most SWG man.'s suggest CYA in the 60-80 range. you'll most likely have to turn your cell down to an even lower setting if you bring the CYA up to that level.

If you do have to shock at some point, I highy recommend doing so with bleach. It keeps the SWG producing in a fixed, stable manner, it saves wear and tear on your cell, and most importantly, brings your FC up in one big dose which makes it much simpler to clear your pool and get rid of excess CC's.

Don't be too surprised if you don't ever get to 1.0 CC's .5 is quite common in a healthy pool and not an indicator that's it's absolutely headed for 1.0 or more. So, you've got CC's less than 1.0, clear water, and (presumably) the ability to hold FC overnight.......That's the three indicators that chemgeek talks about that say you have a healthy pool.

Most SWG man.'s suggest CYA in the 60-80 range. you'll most likely have to turn your cell down to an even lower setting if you bring the CYA up to that level.

I think FAS-DPD test results that consistently show low levels of combined chlorine, absent any other indicators of problems, are often the result of faulty testing procedures. Many people add one too few drops of the R-0871 reagent. Per Taylor's website, "When you think you’ve reached the endpoint, add one more drop of titrant to be certain the color change is permanent. If the color remains unchanged, do not count this last drop." I've found that the Taylor FAS-DPD test will often show 0.2 or 0.5 ppm (depending on the sample size) combined chlorine unless you follow that procedure exactly.

I think FAS-DPD test results that consistently show low levels of combined chlorine, absent any other indicators of problems, are often the result of faulty testing procedures. Many people add one too few drops of the R-0871 reagent. Per Taylor's website, "When you think you’ve reached the endpoint, add one more drop of titrant to be certain the color change is permanent. If the color remains unchanged, do not count this last drop." I've found that the Taylor FAS-DPD test will often show 0.2 or 0.5 ppm (depending on the sample size) combined chlorine unless you follow that procedure exactly.

Thanks KurtV. I have always followed the "one additional drop" method and yesterday & today's test were the first times that I've ever registered any CC. I'll see how it goes over the next few days.
Thanks again all!

Thanks KurtV. I have always followed the "one additional drop" method and yesterday & today's test were the first times that I've ever registered any CC. I'll see how it goes over the next few days.
Thanks again all!

KurtV - I don't want you to throw away your theory that quickly. I'm a rookie at this testing thing so there's a strong chance that you are still on the money!

When I tested this morning I paid close attention to the drops and colors.

I add the DPD to the pool water sample - it turns bright pink. (Woo-hoo I have FC!)
The first 10 drops of FAS do nothing to change that color. (Already I know it's not come down as much as I would like)
11 - pink color getting lighter (hmmmm)
12 - pink color getting lighter (this is going to be close)
13 - pink color getting lighter (I don't like this, it's not come down much at all)
14 - pink color getting lighter, almost gone (aggghhh, it's not come down any!)
15 - solution now just looks misty, a really faint tinge of pink (maybe I am imagining it!)
16 - it's clear - so my FC is 8.0 (dammit!!! It's still going up, need to rack the SWCG down even more!!!)
17 - this is the extra drop. Solution stays clear. Maybe it's even clearer, maybe I'm imagining it!

Add 5 drops of the R-0003.
The solution now looks like it did after 15 drops of FAS.
It's not bright pink, no way near, but there was a change, it's not clear anymore and so I add a drop of FAS and it goes back to being clear. That's why I figure I have CC of 0.5. Am I wrong?

I know this is pretty detailed - but y'all seem to like that approach and having been here for a few weeks, so do I

One problem is that if you add the extra drop after it's clear just to make sure there is no change, then that reagent hangs around for the Combined Chlorine part of the test essentially counting as one drop towards that test (as was stated earlier, you don't count the extra drop for the FC test, but it should count towards the CC test). Since the turning clear in the chlorine test is usually pretty obvious (after you get used to it), I stop and count when it turns clear, then add the 5 drops of R-0003. At this point it usually turns the faintest of pink -- just a hint of it. If I add one drop of FAS reagent, it turns clear which tells me there is less than 0.2 ppm CC. That's my experience.

So my suggestion for this "2-in-1" test for FC and CC is that you either don't do the extra drop after it turns clear, or if you do the extra drop then if the color doesn't change, do not count it towards FC but do count it towards the CC so if adding 5 drops has it stay clear, then that means less than 0.2 ppm CC (in my case). It's 0.2 ppm and not 0.5 ppm because I am using a 25 ml sample size. You can do that with your TF100 test kit as well, even though the instructions talk about using a 10 ml sample size. That might get you more accuracy with the CC level which might actually be only 0.2 (or less) instead of 0.5. With the 25 ml sample size, each drop represents 0.2 ppm (divide drops by 5) compared with the 10 ml sample where each drop represents 0.5 ppm (divide drops by 2). You might need to use 2 scoops instead of 1 of the DPD powder for the larger 25 ml sample size -- I'm not sure about that, but would guess that would be best.

You need enough DPD powder to turn the sample pink. The exact amount required varies with both the sample size and the FC level. Convienently, having a bit too much doesn't really matter, so there is no need to measure accurately. Taylor says two scoops and then add more if it goes brown, Ben says one scoop (but his scoop is larger), Duraleigh says one heaping scoop and add more if it doesn't turn pink.